CFITSIO - A FITS File Subroutine Library

CFITSIO is a library of C and Fortran subroutines for reading and
writing data files in
FITS
(Flexible Image Transport System) data format.
CFITSIO provides simple high-level routines for reading and writing FITS
files that insulate the programmer from the internal complexities of the
FITS format.
CFITSIO also provides many
advanced features
for manipulating and filtering the information in FITS files.